Paper conveyance apparatus for an image forming apparatus and a method thereof

ABSTRACT

A paper conveyance apparatus and method for an image forming apparatus are disclosed. The paper conveyance apparatus and method provide an improved structure in which when the distance between the conveyance roller shaft and the reversible roller shaft is shortened due to the abrasion of the reversible roller, the center of a gear train which transmits a driving force to the reversible roller is swung to move as much as the shortened distance so that the reversible roller can be continuously in contact with the conveyance roller. The paper conveyance apparatus and method comprise a conveyance roller for conveying a paper sheet to an image forming section, a reversible roller for contacting the conveyance roller, a driving motor having a driving gear for supplying a driving force to the reversible roller, and an idle gear for transmitting a driving force from the driving motor to the reversible roller. The center of rotation of the idle gear is movable according to the degree of abrasion of the reversible roller in order to transmit a driving force from the driving motor to the reversible roller.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(a) of KoreanApplication No. 2003-93183, filed Dec. 18, 2003, in the KoreanIntellectual Property Office, the entire contents of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus. Moreparticularly, the present invention relates to a paper feeder and methodfor an image forming apparatus, for reducing the malfunction caused byabrasion of a reversible roller that rotates forwards and backwards incontact with a conveyance roller so that paper sheets are picked up oneby one.

2. Description of the Related Art

FIG. 1 is a diagram illustrating a conventional electrophotographicimage forming apparatus 1 which feeds a paper P using a knock-up platetype of a feeding device 2. As shown in FIG. 1, a paper P is picked upby a pickup roller. A conveyance apparatus 10 having a plurality ofrollers is provided to prevent the simultaneous feeding of two or morepaper sheets.

As shown in FIG. 2, the conveyance apparatus 10 consists of a conveyanceroller 11 and a reversible roller 12. A torque limiter 13 is mounted onthe same axis of the reversible roller 12. Also, a reversible motor (notshown) for reversely rotating the reversible roller 12 is providedindependently from a driving device for rotating the conveyance roller11.

The reversible roller 12 rotates in an opposite direction to theconveyance roller 11. When two or more paper sheets are fed at once, thereversible roller 12 separates the top paper sheet from the underlyingpaper sheets using a difference in the coefficient of friction betweenthe reversible roller 12 and the conveyance roller 11. When a singlepaper sheet is fed, the friction force between the conveyance roller 11and the reversible roller 12 becomes greater than a predetermined torqueof the coaxial torque limiter 13, thereby making the reversible roller12 rotate in the same direction of the rotation of the conveyance roller11. A reversible gear 14 is also mounted on the same axis of thereversible roller 12 to receive a driving force from the reversiblemotor. The reversible gear 14 rotates in a direction opposite to thedirection of rotation of the torque limiter 13, and operatesindependently from the rotation of the conveyance roller 11.

The conveyance roller 11 and the reversible roller 12 comprise a rubberhaving a predetermined solidity, friction coefficient and durability,such as a Natural Rubber (NR), an Acrylonitrile Butadiene Rubber (NBR),an Ethylene-Proplyene-Diene (EPDM), a urethane or a silicon.

Since the reversible roller 12 rotates in the opposite direction to apaper feeding direction, the surface of the reversible roller 12contacting the conveyance roller 11 is apt to be easily abraded. As thesurface of the reversible roller 12 becomes abraded, a conveyance rollershaft S1 and a reversible roller shaft S2 are not maintained in parallelwith each other but form an incline, as shown in FIG. 2. This problemresults from the fixed position of the reversible gear 14. When theconveyance roller shaft S1 and the reversible roller shaft S2 are not inparallel with each other, the conveyance roller 11 and the reversibleroller 12 do not contact sufficiently to separate two or more papersheets fed together and smoothly feed the paper sheets sequentially.Accordingly, the abrasion of the reversible roller 12 may cause errorsin the operation of the image forming apparatus.

SUMMARY OF THE INVENTION

An aspect of the present invention is to solve at least the aboveproblems and to provide at least the advantages described below.Accordingly, an aspect of the present invention is to provide a paperfeeder and method for an image forming apparatus, having an improvedstructure to reduce the malfunction caused by abrasion of a reversibleroller that rotates forwards and backwards in contact with a conveyanceroller so that paper sheets are picked up sequentially.

In order to achieve the above-described aspects of the presentinvention, there is provided a paper feeder and method for an imageforming apparatus. The paper feeder and method comprise a conveyanceroller, a reversible roller, a driving motor and an idle gear. Theconveyance roller and the reversible roller, being in contact with eachother, rotate in the same direction as or the opposite direction to adirection of paper feed to convey paper sheets to an image formingsection, separating paper sheets which are fed together. The reversibleroller is transmitted with a driving force by the driving motor which isseparate from the conveyance roller. In order to transmit the drivingforce, a gear train including an idle gear is used. The center ofrotation of the idle gear is movable so that a contacting force betweenthe conveyance roller and the reversible roller can be kept over apredetermined level even when the reversible roller is abraded.

The idle gear is preferable movable along a track which is a part of thecircumference of a virtual circle having a radius corresponding to thedistance between the center of the driving gear and the center of theidle gear.

The central shaft of the idle gear may move along a swing slot formed onone sidewall of the image forming apparatus to correspond to the swingtrack of the idle gear.

According to a first embodiment of the present invention, the swing slothas an inner periphery with a curvature corresponding to the curvedswing track of the idle gear.

According to a second embodiment of the present invention, the swingslot is formed in a direction of a tangent to a virtual circle having aradius corresponding to the distance between the center of the drivinggear and the center of the idle gear. The swing slot may include anelastic member for elastically supporting the central shaft of the idlegear.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the presentinvention will become more apparent from the following detaileddescription taken with the accompanying drawings in which:

FIG. 1 is a diagram illustrating a conventional image forming apparatus;

FIG. 2 is a diagram illustrating a state in which a conveyance rollerand a reversible roller of the conventional image forming apparatus areinclined due to abrasion of the reversible roller;

FIG. 3 is a diagram illustrating a state in which rotation shafts of aconveyance roller and a reversible roller according to an embodiment ofthe present invention move in response to the abrasion of a reversibleroller;

FIG. 4 is a diagram illustrating a sectional view of an arrangement ofgears, motors and shafts according to an embodiment of the presentinvention;

FIG. 5 is a diagram illustrating a gear train of a reversible rolleraccording to a first embodiment of the present invention; and

FIG. 6 is a diagram illustrating a gear train of a reversible rolleraccording to a second embodiment of the present invention.

Throughout the drawings, it should be noted that the same or similarelements are denoted by like reference numerals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a few embodiments of a paper conveyance apparatus andmethod for an image forming apparatus according to embodiments of thepresent invention will now be described in detail with reference to theaccompanying drawings.

FIG. 3 is a diagram illustrating a paper feeder according to anembodiment of the present invention.

As shown in FIG. 3, the conveyance apparatus 100 includes a conveyanceroller 110, and a reversible roller 120 pressed against the conveyanceroller 110 at a predetermined pressure. In order to rotate theconveyance roller 110 and the reversible roller 120, a conveyance gear112 and a reversible gear 122 are provided to receive a driving forcefrom respective driving sources (not shown).

A load regulator having a torque limiter T coaxial to the reversibleroller 120 is mounted on a reversible roller shaft 121. The torquelimiter T detects whether the friction force between the conveyanceroller 110 and the reversible roller 120 is reduced by a paper sheet fedbetween the two rollers 110 and 120 to a level below a predeterminedfriction coefficient. When a single paper sheet is fed, the reversibleroller 120 rotates in the same direction as the conveyance roller 110 toconvey the paper. When two or more paper sheets are fed at once, thereversible roller 120 rotates in an opposite direction to the conveyanceroller 110 according to a detection signal from the torque limiter T inorder to separate the fed paper sheets so that only the top paper sheetis conveyed to an image forming section.

More specifically, a paper picked up by a pickup roller is fed betweenthe conveyance roller 110 and the reversible roller 120, and conveyed tothe image forming section. If the friction between the conveyance roller110 and the reversible roller 120 is greater than a predeterminedcoefficient of friction, the reversible roller 120 rotates in the samedirection of the rotation of the conveyance roller 110. In contrast, ifthe friction is smaller than the predetermined coefficient of friction,the reversible roller 120 rotates in the opposite direction. The longerthe reversible roller 120 is used, the more it becomes abraded due tofriction with the conveyance roller 110. With the increase of theabrasion of the reversible roller 120, the reversible roller shaft 121moves parallel by a distance ‘d’ toward the conveyance roller shaft 110as shown in FIGS. 3 and 4. Therefore, in order to continuously transmita driving force to the reversible roller 120 from a driving motor 130(FIG. 4), an idle gear 140 is required, which flexibly moves to be keptin mesh with the reversible gear 122 even when the position of thereversible roller shaft 121 is changed. As shown in FIG. 4, the centralshaft Ci of the idle gear 140 is designed to be movable.

The central shaft Ci of the idle gear 140 moves along a swing track A asshown in FIG. 4 to maintain the idle gear 140 and the reversible gear122 in mesh. The central shaft Ci of the idle gear 140 is slidablymounted on one sidewall W (FIGS. 5 and 6) of the image formingapparatus. When the reversible roller shaft 121 moves parallel towardthe conveyance roller shaft 111, the central shaft Ci also moves alongthe swing track A to maintain the idle gear 140 and the reversible gear120 in mesh. The swing track A may be a part of the circumference of avirtual circle having a radius corresponding to the distance between thecentral shaft Cm of the driving gear 131 and the central shaft Ci of theidle gear 140.

FIGS. 5 and 6 are diagrams illustrating the idle gear 140 with thecentral shaft Ci movable along the swing track A according to first andsecond embodiments of the present invention.

In accordance with the first embodiment of the present invention, thecentral shaft Ci of the idle gear 140 is slidably mounted on onesidewall W of the image forming apparatus. For this, the sidewall W hasa curved swing slot 141 having a curvature corresponding to the swingtrack A and a width corresponding to the diameter of the central shaftCi. Accordingly, when the position of the reversible roller shaft 121 ischanged due to the abrasion of the reversible roller 120, the centralshaft Ci slides along the swing slot 141 to maintain the idle gear 140and the reversible gear 122 in mesh.

As shown in FIG. 5, the curved swing slot 141 has a width correspondingto the diameter of the central shaft Ci of the idle gear 140. Also, theswing slot 141 has a curvature corresponding to the curved swing trackA.

According to the second embodiment of the present invention, the centralshaft Ci of the idle gear 140 is slidably mounted on one sidewall W ofthe image forming apparatus. In this connection, the sidewall W has astraight swing slot 142 formed in a direction of a tangent to the swingtrack A, and having a width corresponding to the diameter of the centralshaft Ci. An elastic member 143 such as a compression spring is mountedwithin the swing slot 142. The elastic member 143 exerts an elasticrestoring force so that the idle gear 140 can be maintained in mesh withthe reversible gear 122.

In the paper conveyance apparatus 100 for an image forming apparatusaccording to the first and second embodiments of the present invention,when the reversible roller 120 is abraded, the reversible roller shaft121 moves parallel toward the conveyance roller 110 by a distancecorresponding the abraded thickness of the reversible roller 120,thereby preventing a biased abrasion of the reversible roller 120 andany error of feeding plural paper sheets at once.

When the distance between the conveyance roller shaft 111 and thereversible roller shaft 121 is shortened due to the abrasion of thereversible roller 120, the idle gear 140 for transmitting the drivingforce to the reversible roller 120 is swung to move upward as much asthe shortened distance so that the reversible roller 120 can beconstantly in contact with the conveyance roller 110. Accordingly, byeliminating any causes of biased abrasion of the reversible roller 120,reliability of the image forming apparatus is ensured.

While the invention has been shown and described with reference tocertain embodiments thereof, it should be understood by those skilled inthe art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the invention as definedby the appended claims.

1. A paper conveyance apparatus for an image forming apparatus, comprising: a conveyance roller for conveying a paper sheet to an image forming section; a reversible roller for contacting the conveyance roller; a driving motor having a driving gear for supplying a driving force to the reversible roller; and an idle gear for transmitting a driving force from the driving motor to the reversible roller, wherein the center of rotation of the idle gear is movable according to the degree of abrasion of the reversible roller in order to transmit a driving force from the driving motor to the reversible roller.
 2. The paper conveyance apparatus according to claim 2, wherein the idle gear is movable along a track which is a part of the circumference of a virtual circle having a radius corresponding to a distance between the center of the driving gear and the center of the idle gear.
 3. The paper conveyance apparatus according to claim 2, wherein a central shaft of the idle gear is movable along a swing slot formed on one sidewall of the image forming apparatus to correspond to the swing track of the idle gear.
 4. The paper conveyance apparatus according to claim 3, wherein the swing slot has an inner periphery with a curvature corresponding to the swing track of the idle gear.
 5. The paper conveyance apparatus according to claim 3, wherein the swing slot is formed in a direction of a tangent to a virtual circle having a radius corresponding to the distance between the center of the driving gear and the center of the idle gear.
 6. The paper conveyance apparatus according to claim 5, wherein the swing slot comprises an elastic member for elastically supporting the central shaft of the idle gear.
 7. A method of feeding paper in an image forming apparatus, comprising: conveying a paper sheet to an image forming section via a conveyance roller; contacting the conveyance roller via a reversible roller; supplying a driving force to the reversible roller via a driving motor having a driving gear; and transmitting a driving force from the driving motor to the reversible roller via an idle gear, wherein the center of rotation of the idle gear is movable according to the degree of abrasion of the reversible roller in order to transmit a driving force from the driving motor to the reversible roller.
 8. The method according to claim 7, wherein the idle gear is movable along a track which is a part of the circumference of a virtual circle having a radius corresponding to a distance between the center of the driving gear and the center of the idle gear.
 9. The method according to claim 8, further comprising: providing a central shaft of the idle gear which is movable along a swing slot formed on one sidewall of the image forming apparatus to correspond to the swing track of the idle gear.
 10. The method according to claim 9, wherein the swing slot has an inner periphery with a curvature corresponding to the swing track of the idle gear.
 11. The method according to claim 9, wherein the swing slot is formed in a direction of a tangent to a virtual circle having a radius corresponding to the distance between the center of the driving gear and the center of the idle gear.
 12. The method according to claim 11, wherein the swing slot comprises an elastic member for elastically supporting the central shaft of the idle gear. 